As part of a retrospective season dedicated to that utterly unique English actor Dirk Bogarde, BFI Southbank is this week screening his 1961 film Victim. Bogarde stars as Melville Farr, a brilliant, upwardly mobile barrister with a dark past: he's an in-the-closet gay man who risks exposure (in the days when it was illegal) by taking on a homosexual blackmail ring. It was co-written by Janet Green – a thriller/whodunnit specialist who counted Midnight Lace among her credits – and directed by Basil Dearden.

What a gripping film – melodramatic and self-conscious, yes, but forthright and bold. Its tendency to show homosexuality as a tragic, pitiable quirk of nature may now look like condescension, but for the time this was real risk-taking. It has some of the earnestness of the traditional "issue" movie, but it's also a drum-tight thriller with a neat twist in the tail. Some characters, notably a kindly liberal police inspector, voice rather elaborate campaigning sentiments about how the unreformed law is just a blackmailers' charter. But there's some succinct point-making too: the same inspector, bemused by his sergeant's loathing of homosexuals, reminds him that puritanism was once against the law as well.

For all this, however, it could be that Victim may come to be valued, 50 years on, not as a study of homosexuality, but of blackmail and paranoia.

The word "homosexuality" is not said aloud in Victim until around 30 minutes in; until that time, there is indeed something elliptical and mysterious – Pinteresque, even – about all these men flinching and wincing at sudden phonecalls, visits and scrawled letters. But I realised that it reminded me of someone quite other than Pinter. In an opening scene, Farr's brother-in-law, a widower with a young son, worries about packing the boy off to boarding school: it looks and sounds like The Winslow Boy, and in fact the whole movie, with its elegance, the craftsmanship of its plot, and the gallant extension of sympathy towards female characters, does look like something by Terence Rattigan.

Rattigan famously took gay themes and story lines and prudently "heterosexualised" them. If he had tackled homosexuality head on, Victim is the kind of stage-play or screenplay he might have produced. Melville Farr himself is, tellingly, not actually guilty of the criminal act itself: it appears he had a passionate, unconsummated infatuation with a young man at university. His young wife, played by Sylvia Sims, forgave him for this before their wedding and trusts that these tendencies are a thing of the past. A liaison (again unconsummated) with a young building-site worker, shows that they aren't.

Bogarde is lit and made up to look more of a drawn and haunted figure than he actually was – particularly so in the agonised and very shadowy scenes in which his wife confronts him. Interviews from the time show a much younger, animated-looking Bogarde, almost as boyish as his Simon Sparrow persona.

There is in the film a good deal of the world of Patrick Hamilton – another writer I always find myself coming back to in writing about British movies of this era. This is the seedy, nasty world of pubs and drinking holes around Cecil Court, St Martin's Lane and the Charing Cross Road in London's West End. The blind man and his creepy amanuensis are inspired characters, unforgettably disturbing and unpleasant, sitting in the corner of the pub, parasitically soaking in all the neurotic whisperings. Perhaps the blind man is inspired by Tiresias in TS Eliot's The Waste Land, foresuffering all the cheap and sordid goings-on. Or perhaps he is that sinister West End figure that the paranoid Harold Wilson talked about in 1976 when he told Sunday Times reporter Barrie Penrose: "Occasionally when we meet I might tell you to go to the Charing Cross Road and kick a blind man standing on the corner. That blind man might tell you something, lead you somewhere." It is perhaps in its evocation of the strange, occult world of blackmail, conspiracy and shame, and the seediness of a certain type of London, that Victim holds up best.